Laserfiche WebLink
<br />were used and the discharge-drainage area curves were developed <br />for the 10-, 50-, 100-, 500-year irecurrence intervals. <br /> <br />Peak discharge-drainage area rel~tionships for the streams studied <br />in Pitkin COunty are shown in Ta~le 2. Only 100-year frequency <br />discharges are reported for the reaches to be studied by approximate <br />methods. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out:to provide estimates of the ele- <br />vations of floods of the selecte9 recurrence intervals. <br /> <br />Water-surface elevations were computed using the COE HEC-2 step-back- <br />water computer program (Reference 11). <br /> <br />Cross section data for the backwater analysis of streams within <br />pitkin County were obtained from 'topographic maps as follows: Roaring <br />Fork River (References 12 and 13)! 1 Maroon Creek (Reference 3) 1 <br />Hunter Creek and Castle Creek (R~ference 12)1 Brush Creek (Refer- <br />ence 14)1 and Crystal River and qoal Creek (Reference 18). Cross <br />sections for the Fryingpan River~ Snowmass Creek, and portions of <br />the Crystal and Roaring Fork Rivers were digitized from aerial <br />photographs (References 17, 18, 19, and 20). Parts of Brush Creek <br />and the Roaring Fork and Fryingpan Rivers were field surveyed to <br />obtain additional cross section data. All bridges and culverts <br />were field surveyed to obtain el~vation data and structural geometry. <br /> <br />Locations of selected cross sect~ons used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For stream segments <br />for which a floodway was compute4 (Section 4.2), selected cross <br />section locations are also shown:on the Flood Insurance Rate Map <br />(Exhibit 2). <br /> <br />Roughness factors (Manning's On") used in the hydraulic computations <br />were chosen by engineering judgment and based on field observations <br />of the streams and flood plain a~eas. The ranges of roughness <br />values for detailed-study stream~ were as follows: <br /> <br />Streams <br />Brush Creek <br />Castle Creek <br />Coal Creek <br />Crystal River <br />Hunter Creek <br />Maroon Creek <br />Roaring Fork Creek <br />Snowmass Creek <br />Fryingpan River <br /> <br />ci:hannel <br />0,040-0.050 <br />'0.045 <br />OJ040-0.050 <br />OJ035-0.055 <br />:0.040 <br />'0.045 <br />Ol035-0.045 <br />Ol040-0.045 <br />01035-0.080 <br /> <br />Overbank <br />0.060-0.070 <br />0.080-0.100 <br />0.060-0.080 <br />0.050-0.085 <br />0.080 <br />0.060-0.080 <br />0.045-0.150 <br />0.060-0.070 <br />0.035-0.100 <br /> <br />14 <br />